FIG. 2 shows a conventional gas discharge light apparatus 10 having a gas discharge lamp 11, which in this case is a conventional fluorescent lamp. The fluorescent lamp 11 includes an elongate glass tube 12 having sealed in opposite ends respective filaments 13 and 14 which serve as spaced electrodes within the interior of the tube. The interior of the tube is coated with phosphors. The interior of the tube contains a gas or vapor such as mercury vapor, along with a few ions. One end of the tube has two external terminals 16 and 17 which are connected to respective ends of the filament 13, and the other end of the tube 12 has two external terminals 18 and 19 which are connected to respective ends of the filament 14.
A standard plug 21 is of the type which can be connected to any standard 120 volt 60 Hz AC wall outlet, and the plug 21 is connected in series with a choke 22 between the terminals 16 and 18 of the lamp 11. The choke 22 is often referred to as a ballast. A thermal switch 23 is disposed within a neon bulb 26 and is connected in series with a resistor 27 between the terminals 17 and 19 of the lamp 11, the thermal switch 23 normally being closed and opening automatically when its temperature increases above a predetermined temperature. The spaced internal terminals of the neon bulb 26 are connected in series with resistor 27 between the terminals 17 and 19.
When the apparatus has been off for a period of time, the switch 23 will be closed. The gas in the lamp 11 will contain a minimum of ions, and will thus be substantially non-conductive. If the plug 21 is then inserted into a wall outlet, AC current will flow through electrode 13, closed switch 23, electrode 14 and choke 22. This heats the filaments 13 and 14, causing them to emit electrons within the tube. After a predetermined time, heat generated by components of the system will cause the thermal switch 23 to open, thereby interrupting the AC circuit. Because of the magnetic field around the choke 22, the choke 22 will produce a high voltage across the electrodes 13 and 14, which causes positive ions to move toward one of the electrodes and negative ions to move toward the other electrode. These ions collide with neutral atoms and impart energy to electrons of the neutral atoms, which causes the electrons to gain energy and to be displaced to an exterior orbit, the electrons eventually giving up their acquired energy in the form of electromagnetic radiation which in some cases is in a short-wave ultraviolet range which the phosphors coating the tube convert into visible light, so that the lamp 11 emits light. Some electrons will be displaced entirely from the neutral atoms, thus generating additional ions which can collide with other neutral atoms in order to increase the amount of visible light generated. The significantly increased level of ionization means the lamp 11 is now conductive.
After the momentary voltage surge from the choke 22 which ionized the gas in the lamp 11 has dissipated, the lamp will continue to operate under standard 120 volt AC power. The discharge is extinguished twice per cycle when the AC voltage is at zero, but the instantaneous restarting of the discharge requires a much lower voltage than the initial starting voltage because the majority of the ions have not had time to recombine with atoms so as to return the ion density to its original level. After the switch 23 has opened, power is applied to the neon bulb 26 and causes it to light and give off heat, the heat causing the thermal switch 23 to remain open.
Although the arrangement shown in FIG. 2 has been adequate for its intended purposes, it has not been satisfactory in all respects. In particular, it will be immediately recognized that, if one of the electrode filaments 13 or 14 burns out, the resulting open will interrupt the starting circuit and thus ionization and initiation of the discharge will not take place. Alternatively, if the input voltage at line 21 is low or if the ambient temperature is low, it can be difficult or impossible to initiate discharge from the lamp 11. Also, the predetermined time required for the thermal switch 23 to heat up and open means that the lamp does not start instantaneously. Moreover, during operation, the arrangement shown in FIG. 2 has a lagging power factor, and may tend to produce an annoying audible hum. Also, the choke 22 tends to produce heat which, over time, can cause the choke 22 to fail, often with the generation of obnoxious smells. In addition, the choke 22 is relatively large and heavy, and the overall starter circuit is thus not compact and lightweight.
Another known approach is to rectify and filter a standard 120 volt AC signal in order to produce a DC signal, and to use the DC signal to power a circuit which includes a 25 KHz oscillator, the resulting 25 KHz signal being applied to the gas discharge lamp in order to produce excitation which initiates ionization and discharge. However, the use of a 25 KHz signal means that the device must be approved by the Federal Communications Commission (FCC), and even with approval it may generate electromagnetic fields which will interfere with the operation of other devices such as radios, televisions, and computers. Because of these disadvantages, this approach is not widely used, and is not illustrated or described in further detail here.
An object of the invention is to provide a starter circuit for a gas discharge lamp which will reliably light the lamp in a substantially instantaneous manner even at relatively low line voltages, and which produces no noticeable flicker.
A further object is to provide such a starter circuit which avoids the use of a transformer or a ballast or choke, and which is relative compact.
It is a further object to provide such a starter circuit which generates minimal heat and which transfers power with a high level of efficiency from a power source to the lamp.
It is a further object to provide such a starter circuit which, in the case of a lamp such as a standard fluorescent light having one or more internal electrode filaments connected between respective external terminals, can reliably and substantially instantaneously initiate ionization and discharge even when the filament is broken.
A further object is to provide such a starter circuit which is inexpensive, requires no maintenance, and has a long operational lifetime.